/lib/enrollib.php

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<?php

// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * This library includes the basic parts of enrol api.
 * It is available on each page.
 *
 * @package    core
 * @subpackage enrol
 * @copyright  2010 Petr Skoda {@link http://skodak.org}
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();

/** Course enrol instance enabled. (used in enrol->status) */
define('ENROL_INSTANCE_ENABLED', 0);

/** Course enrol instance disabled, user may enter course if other enrol instance enabled. (used in enrol->status)*/
define('ENROL_INSTANCE_DISABLED', 1);

/** User is active participant (used in user_enrolments->status)*/
define('ENROL_USER_ACTIVE', 0);

/** User participation in course is suspended (used in user_enrolments->status) */
define('ENROL_USER_SUSPENDED', 1);

/** @deprecated - enrol caching was reworked, use ENROL_MAX_TIMESTAMP instead */
define('ENROL_REQUIRE_LOGIN_CACHE_PERIOD', 1800);

/** The timestamp indicating forever */
define('ENROL_MAX_TIMESTAMP', 2147483647);

/** When user disappears from external source, the enrolment is completely removed */
define('ENROL_EXT_REMOVED_UNENROL', 0);

/** When user disappears from external source, the enrolment is kept as is - one way sync */
define('ENROL_EXT_REMOVED_KEEP', 1);

/** @deprecated since 2.4 not used any more, migrate plugin to new restore methods */
define('ENROL_RESTORE_TYPE', 'enrolrestore');

/**
 * When user disappears from external source, user enrolment is suspended, roles are kept as is.
 * In some cases user needs a role with some capability to be visible in UI - suc has in gradebook,
 * assignments, etc.
 */
define('ENROL_EXT_REMOVED_SUSPEND', 2);

/**
 * When user disappears from external source, the enrolment is suspended and roles assigned
 * by enrol instance are removed. Please note that user may "disappear" from gradebook and other areas.
 * */
define('ENROL_EXT_REMOVED_SUSPENDNOROLES', 3);

/**
 * Do not send email.
 */
define('ENROL_DO_NOT_SEND_EMAIL', 0);

/**
 * Send email from course contact.
 */
define('ENROL_SEND_EMAIL_FROM_COURSE_CONTACT', 1);

/**
 * Send email from enrolment key holder.
 */
define('ENROL_SEND_EMAIL_FROM_KEY_HOLDER', 2);

/**
 * Send email from no reply address.
 */
define('ENROL_SEND_EMAIL_FROM_NOREPLY', 3);

/** Edit enrolment action. */
define('ENROL_ACTION_EDIT', 'editenrolment');

/** Unenrol action. */
define('ENROL_ACTION_UNENROL', 'unenrol');

/**
 * Returns instances of enrol plugins
 * @param bool $enabled return enabled only
 * @return array of enrol plugins name=>instance
 */
function enrol_get_plugins($enabled) {
    global $CFG;

    $result = array();

    if ($enabled) {
        // sorted by enabled plugin order
        $enabled = explode(',', $CFG->enrol_plugins_enabled);
        $plugins = array();
        foreach ($enabled as $plugin) {
            $plugins[$plugin] = "$CFG->dirroot/enrol/$plugin";
        }
    } else {
        // sorted alphabetically
        $plugins = core_component::get_plugin_list('enrol');
        ksort($plugins);
    }

    foreach ($plugins as $plugin=>$location) {
        $class = "enrol_{$plugin}_plugin";
        if (!class_exists($class)) {
            if (!file_exists("$location/lib.php")) {
                continue;
            }
            include_once("$location/lib.php");
            if (!class_exists($class)) {
                continue;
            }
        }

        $result[$plugin] = new $class();
    }

    return $result;
}

/**
 * Returns instance of enrol plugin
 * @param  string $name name of enrol plugin ('manual', 'guest', ...)
 * @return enrol_plugin
 */
function enrol_get_plugin($name) {
    global $CFG;

    $name = clean_param($name, PARAM_PLUGIN);

    if (empty($name)) {
        // ignore malformed or missing plugin names completely
        return null;
    }

    $location = "$CFG->dirroot/enrol/$name";

    $class = "enrol_{$name}_plugin";
    if (!class_exists($class)) {
        if (!file_exists("$location/lib.php")) {
            return null;
        }
        include_once("$location/lib.php");
        if (!class_exists($class)) {
            return null;
        }
    }

    return new $class();
}

/**
 * Returns enrolment instances in given course.
 * @param int $courseid
 * @param bool $enabled
 * @return array of enrol instances
 */
function enrol_get_instances($courseid, $enabled) {
    global $DB, $CFG;

    if (!$enabled) {
        return $DB->get_records('enrol', array('courseid'=>$courseid), 'sortorder,id');
    }

    $result = $DB->get_records('enrol', array('courseid'=>$courseid, 'status'=>ENROL_INSTANCE_ENABLED), 'sortorder,id');

    $enabled = explode(',', $CFG->enrol_plugins_enabled);
    foreach ($result as $key=>$instance) {
        if (!in_array($instance->enrol, $enabled)) {
            unset($result[$key]);
            continue;
        }
        if (!file_exists("$CFG->dirroot/enrol/$instance->enrol/lib.php")) {
            // broken plugin
            unset($result[$key]);
            continue;
        }
    }

    return $result;
}

/**
 * Checks if a given plugin is in the list of enabled enrolment plugins.
 *
 * @param string $enrol Enrolment plugin name
 * @return boolean Whether the plugin is enabled
 */
function enrol_is_enabled($enrol) {
    global $CFG;

    if (empty($CFG->enrol_plugins_enabled)) {
        return false;
    }
    return in_array($enrol, explode(',', $CFG->enrol_plugins_enabled));
}

/**
 * Check all the login enrolment information for the given user object
 * by querying the enrolment plugins
 *
 * This function may be very slow, use only once after log-in or login-as.
 *
 * @param stdClass $user
 * @return void
 */
function enrol_check_plugins($user) {
    global $CFG;

    if (empty($user->id) or isguestuser($user)) {
        // shortcut - there is no enrolment work for guests and not-logged-in users
        return;
    }

    // originally there was a broken admin test, but accidentally it was non-functional in 2.2,
    // which proved it was actually not necessary.

    static $inprogress = array();  // To prevent this function being called more than once in an invocation

    if (!empty($inprogress[$user->id])) {
        return;
    }

    $inprogress[$user->id] = true;  // Set the flag

    $enabled = enrol_get_plugins(true);

    foreach($enabled as $enrol) {
        $enrol->sync_user_enrolments($user);
    }

    unset($inprogress[$user->id]);  // Unset the flag
}

/**
 * Do these two students share any course?
 *
 * The courses has to be visible and enrolments has to be active,
 * timestart and timeend restrictions are ignored.
 *
 * This function calls {@see enrol_get_shared_courses()} setting checkexistsonly
 * to true.
 *
 * @param stdClass|int $user1
 * @param stdClass|int $user2
 * @return bool
 */
function enrol_sharing_course($user1, $user2) {
    return enrol_get_shared_courses($user1, $user2, false, true);
}

/**
 * Returns any courses shared by the two users
 *
 * The courses has to be visible and enrolments has to be active,
 * timestart and timeend restrictions are ignored.
 *
 * @global moodle_database $DB
 * @param stdClass|int $user1
 * @param stdClass|int $user2
 * @param bool $preloadcontexts If set to true contexts for the returned courses
 *              will be preloaded.
 * @param bool $checkexistsonly If set to true then this function will return true
 *              if the users share any courses and false if not.
 * @return array|bool An array of courses that both users are enrolled in OR if
 *              $checkexistsonly set returns true if the users share any courses
 *              and false if not.
 */
function enrol_get_shared_courses($user1, $user2, $preloadcontexts = false, $checkexistsonly = false) {
    global $DB, $CFG;

    $user1 = isset($user1->id) ? $user1->id : $user1;
    $user2 = isset($user2->id) ? $user2->id : $user2;

    if (empty($user1) or empty($user2)) {
        return false;
    }

    if (!$plugins = explode(',', $CFG->enrol_plugins_enabled)) {
        return false;
    }

    list($plugins1, $params1) = $DB->get_in_or_equal($plugins, SQL_PARAMS_NAMED, 'ee1');
    list($plugins2, $params2) = $DB->get_in_or_equal($plugins, SQL_PARAMS_NAMED, 'ee2');
    $params = array_merge($params1, $params2);
    $params['enabled1'] = ENROL_INSTANCE_ENABLED;
    $params['enabled2'] = ENROL_INSTANCE_ENABLED;
    $params['active1'] = ENROL_USER_ACTIVE;
    $params['active2'] = ENROL_USER_ACTIVE;
    $params['user1']   = $user1;
    $params['user2']   = $user2;

    $ctxselect = '';
    $ctxjoin = '';
    if ($preloadcontexts) {
        $ctxselect = ', ' . context_helper::get_preload_record_columns_sql('ctx');
        $ctxjoin = "LEFT JOIN {context} ctx ON (ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel)";
        $params['contextlevel'] = CONTEXT_COURSE;
    }

    $sql = "SELECT c.* $ctxselect
              FROM {course} c
              JOIN (
                SELECT DISTINCT c.id
                  FROM {course} c
                  JOIN {enrol} e1 ON (c.id = e1.courseid AND e1.status = :enabled1 AND e1.enrol $plugins1)
                  JOIN {user_enrolments} ue1 ON (ue1.enrolid = e1.id AND ue1.status = :active1 AND ue1.userid = :user1)
                  JOIN {enrol} e2 ON (c.id = e2.courseid AND e2.status = :enabled2 AND e2.enrol $plugins2)
                  JOIN {user_enrolments} ue2 ON (ue2.enrolid = e2.id AND ue2.status = :active2 AND ue2.userid = :user2)
                 WHERE c.visible = 1
              ) ec ON ec.id = c.id
              $ctxjoin";

    if ($checkexistsonly) {
        return $DB->record_exists_sql($sql, $params);
    } else {
        $courses = $DB->get_records_sql($sql, $params);
        if ($preloadcontexts) {
            array_map('context_helper::preload_from_record', $courses);
        }
        return $courses;
    }
}

/**
 * This function adds necessary enrol plugins UI into the course edit form.
 *
 * @param MoodleQuickForm $mform
 * @param object $data course edit form data
 * @param object $context context of existing course or parent category if course does not exist
 * @return void
 */
function enrol_course_edit_form(MoodleQuickForm $mform, $data, $context) {
    $plugins = enrol_get_plugins(true);
    if (!empty($data->id)) {
        $instances = enrol_get_instances($data->id, false);
        foreach ($instances as $instance) {
            if (!isset($plugins[$instance->enrol])) {
                continue;
            }
            $plugin = $plugins[$instance->enrol];
            $plugin->course_edit_form($instance, $mform, $data, $context);
        }
    } else {
        foreach ($plugins as $plugin) {
            $plugin->course_edit_form(NULL, $mform, $data, $context);
        }
    }
}

/**
 * Validate course edit form data
 *
 * @param array $data raw form data
 * @param object $context context of existing course or parent category if course does not exist
 * @return array errors array
 */
function enrol_course_edit_validation(array $data, $context) {
    $errors = array();
    $plugins = enrol_get_plugins(true);

    if (!empty($data['id'])) {
        $instances = enrol_get_instances($data['id'], false);
        foreach ($instances as $instance) {
            if (!isset($plugins[$instance->enrol])) {
                continue;
            }
            $plugin = $plugins[$instance->enrol];
            $errors = array_merge($errors, $plugin->course_edit_validation($instance, $data, $context));
        }
    } else {
        foreach ($plugins as $plugin) {
            $errors = array_merge($errors, $plugin->course_edit_validation(NULL, $data, $context));
        }
    }

    return $errors;
}

/**
 * Update enrol instances after course edit form submission
 * @param bool $inserted true means new course added, false course already existed
 * @param object $course
 * @param object $data form data
 * @return void
 */
function enrol_course_updated($inserted, $course, $data) {
    global $DB, $CFG;

    $plugins = enrol_get_plugins(true);

    foreach ($plugins as $plugin) {
        $plugin->course_updated($inserted, $course, $data);
    }
}

/**
 * Add navigation nodes
 * @param navigation_node $coursenode
 * @param object $course
 * @return void
 */
function enrol_add_course_navigation(navigation_node $coursenode, $course) {
    global $CFG;

    $coursecontext = context_course::instance($course->id);

    $instances = enrol_get_instances($course->id, true);
    $plugins   = enrol_get_plugins(true);

    // we do not want to break all course pages if there is some borked enrol plugin, right?
    foreach ($instances as $k=>$instance) {
        if (!isset($plugins[$instance->enrol])) {
            unset($instances[$k]);
        }
    }

    $usersnode = $coursenode->add(get_string('users'), null, navigation_node::TYPE_CONTAINER, null, 'users');

    if ($course->id != SITEID) {
        // list all participants - allows assigning roles, groups, etc.
        if (has_capability('moodle/course:enrolreview', $coursecontext)) {
            $url = new moodle_url('/user/index.php', array('id'=>$course->id));
            $usersnode->add(get_string('enrolledusers', 'enrol'), $url, navigation_node::TYPE_SETTING, null, 'review', new pix_icon('i/enrolusers', ''));
        }

        // manage enrol plugin instances
        if (has_capability('moodle/course:enrolconfig', $coursecontext) or has_capability('moodle/course:enrolreview', $coursecontext)) {
            $url = new moodle_url('/enrol/instances.php', array('id'=>$course->id));
        } else {
            $url = NULL;
        }
        $instancesnode = $usersnode->add(get_string('enrolmentinstances', 'enrol'), $url, navigation_node::TYPE_SETTING, null, 'manageinstances');

        // each instance decides how to configure itself or how many other nav items are exposed
        foreach ($instances as $instance) {
            if (!isset($plugins[$instance->enrol])) {
                continue;
            }
            $plugins[$instance->enrol]->add_course_navigation($instancesnode, $instance);
        }

        if (!$url) {
            $instancesnode->trim_if_empty();
        }
    }

    // Manage groups in this course or even frontpage
    if (($course->groupmode || !$course->groupmodeforce) && has_capability('moodle/course:managegroups', $coursecontext)) {
        $url = new moodle_url('/group/index.php', array('id'=>$course->id));
        $usersnode->add(get_string('groups'), $url, navigation_node::TYPE_SETTING, null, 'groups', new pix_icon('i/group', ''));
    }

     if (has_any_capability(array( 'moodle/role:assign', 'moodle/role:safeoverride','moodle/role:override', 'moodle/role:review'), $coursecontext)) {
        // Override roles
        if (has_capability('moodle/role:review', $coursecontext)) {
            $url = new moodle_url('/admin/roles/permissions.php', array('contextid'=>$coursecontext->id));
        } else {
            $url = NULL;
        }
        $permissionsnode = $usersnode->add(get_string('permissions', 'role'), $url, navigation_node::TYPE_SETTING, null, 'override');

        // Add assign or override roles if allowed
        if ($course->id == SITEID or (!empty($CFG->adminsassignrolesincourse) and is_siteadmin())) {
            if (has_capability('moodle/role:assign', $coursecontext)) {
                $url = new moodle_url('/admin/roles/assign.php', array('contextid'=>$coursecontext->id));
                $permissionsnode->add(get_string('assignedroles', 'role'), $url, navigation_node::TYPE_SETTING, null, 'roles', new pix_icon('i/assignroles', ''));
            }
        }
        // Check role permissions
        if (has_any_capability(array('moodle/role:assign', 'moodle/role:safeoverride', 'moodle/role:override'), $coursecontext)) {
            $url = new moodle_url('/admin/roles/check.php', array('contextid'=>$coursecontext->id));
            $permissionsnode->add(get_string('checkpermissions', 'role'), $url, navigation_node::TYPE_SETTING, null, 'permissions', new pix_icon('i/checkpermissions', ''));
        }
     }

     // Deal somehow with users that are not enrolled but still got a role somehow
    if ($course->id != SITEID) {
        //TODO, create some new UI for role assignments at course level
        if (has_capability('moodle/course:reviewotherusers', $coursecontext)) {
            $url = new moodle_url('/enrol/otherusers.php', array('id'=>$course->id));
            $usersnode->add(get_string('notenrolledusers', 'enrol'), $url, navigation_node::TYPE_SETTING, null, 'otherusers', new pix_icon('i/assignroles', ''));
        }
    }

    // just in case nothing was actually added
    $usersnode->trim_if_empty();

    if ($course->id != SITEID) {
        if (isguestuser() or !isloggedin()) {
            // guest account can not be enrolled - no links for them
        } else if (is_enrolled($coursecontext)) {
            // unenrol link if possible
            foreach ($instances as $instance) {
                if (!isset($plugins[$instance->enrol])) {
                    continue;
                }
                $plugin = $plugins[$instance->enrol];
                if ($unenrollink = $plugin->get_unenrolself_link($instance)) {
                    $shortname = format_string($course->shortname, true, array('context' => $coursecontext));
                    $coursenode->add(get_string('unenrolme', 'core_enrol', $shortname), $unenrollink, navigation_node::TYPE_SETTING, null, 'unenrolself', new pix_icon('i/user', ''));
                    break;
                    //TODO. deal with multiple unenrol links - not likely case, but still...
                }
            }
        } else {
            // enrol link if possible
            if (is_viewing($coursecontext)) {
                // better not show any enrol link, this is intended for managers and inspectors
            } else {
                foreach ($instances as $instance) {
                    if (!isset($plugins[$instance->enrol])) {
                        continue;
                    }
                    $plugin = $plugins[$instance->enrol];
                    if ($plugin->show_enrolme_link($instance)) {
                        $url = new moodle_url('/enrol/index.php', array('id'=>$course->id));
                        $shortname = format_string($course->shortname, true, array('context' => $coursecontext));
                        $coursenode->add(get_string('enrolme', 'core_enrol', $shortname), $url, navigation_node::TYPE_SETTING, null, 'enrolself', new pix_icon('i/user', ''));
                        break;
                    }
                }
            }
        }
    }
}

/**
 * Returns list of courses current $USER is enrolled in and can access
 *
 * The $fields param is a list of field names to ADD so name just the fields you really need,
 * which will be added and uniq'd.
 *
 * If $allaccessible is true, this will additionally return courses that the current user is not
 * enrolled in, but can access because they are open to the user for other reasons (course view
 * permission, currently viewing course as a guest, or course allows guest access without
 * password).
 *
 * @param string|array $fields Extra fields to be returned (array or comma-separated list).
 * @param string|null $sort Comma separated list of fields to sort by, defaults to respecting navsortmycoursessort.
 * Allowed prefixes for sort fields are: "ul" for the user_lastaccess table, "c" for the courses table,
 * "ue" for the user_enrolments table.
 * @param int $limit max number of courses
 * @param array $courseids the list of course ids to filter by
 * @param bool $allaccessible Include courses user is not enrolled in, but can access
 * @param int $offset Offset the result set by this number
 * @param array $excludecourses IDs of hidden courses to exclude from search
 * @return array
 */
function enrol_get_my_courses($fields = null, $sort = null, $limit = 0, $courseids = [], $allaccessible = false,
    $offset = 0, $excludecourses = []) {
    global $DB, $USER, $CFG;

    // Re-Arrange the course sorting according to the admin settings.
    $sort = enrol_get_courses_sortingsql($sort);

    // Guest account does not have any enrolled courses.
    if (!$allaccessible && (isguestuser() or !isloggedin())) {
        return array();
    }

    $basefields = array('id', 'category', 'sortorder',
                        'shortname', 'fullname', 'idnumber',
                        'startdate', 'visible',
                        'groupmode', 'groupmodeforce', 'cacherev');

    if (empty($fields)) {
        $fields = $basefields;
    } else if (is_string($fields)) {
        // turn the fields from a string to an array
        $fields = explode(',', $fields);
        $fields = array_map('trim', $fields);
        $fields = array_unique(array_merge($basefields, $fields));
    } else if (is_array($fields)) {
        $fields = array_unique(array_merge($basefields, $fields));
    } else {
        throw new coding_exception('Invalid $fields parameter in enrol_get_my_courses()');
    }
    if (in_array('*', $fields)) {
        $fields = array('*');
    }

    $orderby = "";
    $sort    = trim($sort);
    $sorttimeaccess = false;
    $allowedsortprefixes = array('c', 'ul', 'ue');
    if (!empty($sort)) {
        $rawsorts = explode(',', $sort);
        $sorts = array();
        foreach ($rawsorts as $rawsort) {
            $rawsort = trim($rawsort);
            if (preg_match('/^ul\.(\S*)\s(asc|desc)/i', $rawsort, $matches)) {
                if (strcasecmp($matches[2], 'asc') == 0) {
                    $sorts[] = 'COALESCE(ul.' . $matches[1] . ', 0) ASC';
                } else {
                    $sorts[] = 'COALESCE(ul.' . $matches[1] . ', 0) DESC';
                }
                $sorttimeaccess = true;
            } else if (strpos($rawsort, '.') !== false) {
                $prefix = explode('.', $rawsort);
                if (in_array($prefix[0], $allowedsortprefixes)) {
                    $sorts[] = trim($rawsort);
                } else {
                    throw new coding_exception('Invalid $sort parameter in enrol_get_my_courses()');
                }
            } else {
                $sorts[] = 'c.'.trim($rawsort);
            }
        }
        $sort = implode(',', $sorts);
        $orderby = "ORDER BY $sort";
    }

    $wheres = array("c.id <> :siteid");
    $params = array('siteid'=>SITEID);

    if (isset($USER->loginascontext) and $USER->loginascontext->contextlevel == CONTEXT_COURSE) {
        // list _only_ this course - anything else is asking for trouble...
        $wheres[] = "courseid = :loginas";
        $params['loginas'] = $USER->loginascontext->instanceid;
    }

    $coursefields = 'c.' .join(',c.', $fields);
    $ccselect = ', ' . context_helper::get_preload_record_columns_sql('ctx');
    $ccjoin = "LEFT JOIN {context} ctx ON (ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel)";
    $params['contextlevel'] = CONTEXT_COURSE;
    $wheres = implode(" AND ", $wheres);

    $timeaccessselect = "";
    $timeaccessjoin = "";

    if (!empty($courseids)) {
        list($courseidssql, $courseidsparams) = $DB->get_in_or_equal($courseids, SQL_PARAMS_NAMED);
        $wheres = sprintf("%s AND c.id %s", $wheres, $courseidssql);
        $params = array_merge($params, $courseidsparams);
    }

    if (!empty($excludecourses)) {
        list($courseidssql, $courseidsparams) = $DB->get_in_or_equal($excludecourses, SQL_PARAMS_NAMED, 'param', false);
        $wheres = sprintf("%s AND c.id %s", $wheres, $courseidssql);
        $params = array_merge($params, $courseidsparams);
    }

    $courseidsql = "";
    // Logged-in, non-guest users get their enrolled courses.
    if (!isguestuser() && isloggedin()) {
        $courseidsql .= "
                SELECT DISTINCT e.courseid
                  FROM {enrol} e
                  JOIN {user_enrolments} ue ON (ue.enrolid = e.id AND ue.userid = :userid1)
                 WHERE ue.status = :active AND e.status = :enabled AND ue.timestart < :now1
                       AND (ue.timeend = 0 OR ue.timeend > :now2)";
        $params['userid1'] = $USER->id;
        $params['active'] = ENROL_USER_ACTIVE;
        $params['enabled'] = ENROL_INSTANCE_ENABLED;
        $params['now1'] = round(time(), -2); // Improves db caching.
        $params['now2'] = $params['now1'];

        if ($sorttimeaccess) {
            $params['userid2'] = $USER->id;
            $timeaccessselect = ', ul.timeaccess as lastaccessed';
            $timeaccessjoin = "LEFT JOIN {user_lastaccess} ul ON (ul.courseid = c.id AND ul.userid = :userid2)";
        }
    }

    // When including non-enrolled but accessible courses...
    if ($allaccessible) {
        if (is_siteadmin()) {
            // Site admins can access all courses.
            $courseidsql = "SELECT DISTINCT c2.id AS courseid FROM {course} c2";
        } else {
            // If we used the enrolment as well, then this will be UNIONed.
            if ($courseidsql) {
                $courseidsql .= " UNION ";
            }

            // Include courses with guest access and no password.
            $courseidsql .= "
                    SELECT DISTINCT e.courseid
                      FROM {enrol} e
                     WHERE e.enrol = 'guest' AND e.password = :emptypass AND e.status = :enabled2";
            $params['emptypass'] = '';
            $params['enabled2'] = ENROL_INSTANCE_ENABLED;

            // Include courses where the current user is currently using guest access (may include
            // those which require a password).
            $courseids = [];
            $accessdata = get_user_accessdata($USER->id);
            foreach ($accessdata['ra'] as $contextpath => $roles) {
                if (array_key_exists($CFG->guestroleid, $roles)) {
                    // Work out the course id from context path.
                    $context = context::instance_by_id(preg_replace('~^.*/~', '', $contextpath));
                    if ($context instanceof context_course) {
                        $courseids[$context->instanceid] = true;
                    }
                }
            }

            // Include courses where the current user has moodle/course:view capability.
            $courses = get_user_capability_course('moodle/course:view', null, false);
            if (!$courses) {
                $courses = [];
            }
            foreach ($courses as $course) {
                $courseids[$course->id] = true;
            }

            // If there are any in either category, list them individually.
            if ($courseids) {
                list ($allowedsql, $allowedparams) = $DB->get_in_or_equal(
                        array_keys($courseids), SQL_PARAMS_NAMED);
                $courseidsql .= "
                        UNION
                       SELECT DISTINCT c3.id AS courseid
                         FROM {course} c3
                        WHERE c3.id $allowedsql";
                $params = array_merge($params, $allowedparams);
            }
        }
    }

    // Note: we can not use DISTINCT + text fields due to Oracle and MS limitations, that is why
    // we have the subselect there.
    $sql = "SELECT $coursefields $ccselect $timeaccessselect
              FROM {course} c
              JOIN ($courseidsql) en ON (en.courseid = c.id)
           $timeaccessjoin
           $ccjoin
             WHERE $wheres
          $orderby";

    $courses = $DB->get_records_sql($sql, $params, $offset, $limit);

    // preload contexts and check visibility
    foreach ($courses as $id=>$course) {
        context_helper::preload_from_record($course);
        if (!$course->visible) {
            if (!$context = context_course::instance($id, IGNORE_MISSING)) {
                unset($courses[$id]);
                continue;
            }
            if (!has_capability('moodle/course:viewhiddencourses', $context)) {
                unset($courses[$id]);
                continue;
            }
        }
        $courses[$id] = $course;
    }

    //wow! Is that really all? :-D

    return $courses;
}

/**
 * Returns course enrolment information icons.
 *
 * @param object $course
 * @param array $instances enrol instances of this course, improves performance
 * @return array of pix_icon
 */
function enrol_get_course_info_icons($course, array $instances = NULL) {
    $icons = array();
    if (is_null($instances)) {
        $instances = enrol_get_instances($course->id, true);
    }
    $plugins = enrol_get_plugins(true);
    foreach ($plugins as $name => $plugin) {
        $pis = array();
        foreach ($instances as $instance) {
            if ($instance->status != ENROL_INSTANCE_ENABLED or $instance->courseid != $course->id) {
                debugging('Invalid instances parameter submitted in enrol_get_info_icons()');
                continue;
            }
            if ($instance->enrol == $name) {
                $pis[$instance->id] = $instance;
            }
        }
        if ($pis) {
            $icons = array_merge($icons, $plugin->get_info_icons($pis));
        }
    }
    return $icons;
}

/**
 * Returns SQL ORDER arguments which reflect the admin settings to sort my courses.
 *
 * @param string|null $sort SQL ORDER arguments which were originally requested (optionally).
 * @return string SQL ORDER arguments.
 */
function enrol_get_courses_sortingsql($sort = null) {
    global $CFG;

    // Prepare the visible SQL fragment as empty.
    $visible = '';
    // Only create a visible SQL fragment if the caller didn't already pass a sort order which contains the visible field.
    if ($sort === null || strpos($sort, 'visible') === false) {
        // If the admin did not explicitly want to have shown and hidden courses sorted as one list, we will sort hidden
        // courses to the end of the course list.
        if (!isset($CFG->navsortmycourseshiddenlast) || $CFG->navsortmycourseshiddenlast == true) {
            $visible = 'visible DESC, ';
        }
    }

    // Only create a sortorder SQL fragment if the caller didn't already pass one.
    if ($sort === null) {
        // If the admin has configured a course sort order, we will use this.
        if (!empty($CFG->navsortmycoursessort)) {
            $sort = $CFG->navsortmycoursessort . ' ASC';

            // Otherwise we will fall back to the sortorder sorting.
        } else {
            $sort = 'sortorder ASC';
        }
    }

    return $visible . $sort;
}

/**
 * Returns course enrolment detailed information.
 *
 * @param object $course
 * @return array of html fragments - can be used to construct lists
 */
function enrol_get_course_description_texts($course) {
    $lines = array();
    $instances = enrol_get_instances($course->id, true);
    $plugins = enrol_get_plugins(true);
    foreach ($instances as $instance) {
        if (!isset($plugins[$instance->enrol])) {
            //weird
            continue;
        }
        $plugin = $plugins[$instance->enrol];
        $text = $plugin->get_description_text($instance);
        if ($text !== NULL) {
            $lines[] = $text;
        }
    }
    return $lines;
}

/**
 * Returns list of courses user is enrolled into.
 *
 * Note: Use {@link enrol_get_all_users_courses()} if you need the list without any capability checks.
 *
 * The $fields param is a list of field names to ADD so name just the fields you really need,
 * which will be added and uniq'd.
 *
 * @param int $userid User whose courses are returned, defaults to the current user.
 * @param bool $onlyactive Return only active enrolments in courses user may see.
 * @param string|array $fields Extra fields to be returned (array or comma-separated list).
 * @param string|null $sort Comma separated list of fields to sort by, defaults to respecting navsortmycoursessort.
 * @return array
 */
function enrol_get_users_courses($userid, $onlyactive = false, $fields = null, $sort = null) {
    global $DB;

    $courses = enrol_get_all_users_courses($userid, $onlyactive, $fields, $sort);

    // preload contexts and check visibility
    if ($onlyactive) {
        foreach ($courses as $id=>$course) {
            context_helper::preload_from_record($course);
            if (!$course->visible) {
                if (!$context = context_course::instance($id)) {
                    unset($courses[$id]);
                    continue;
                }
                if (!has_capability('moodle/course:viewhiddencourses', $context, $userid)) {
                    unset($courses[$id]);
                    continue;
                }
            }
        }
    }

    return $courses;
}

/**
 * Returns list of roles per users into course.
 *
 * @param int $courseid Course id.
 * @return array Array[$userid][$roleid] = role_assignment.
 */
function enrol_get_course_users_roles(int $courseid) : array {
    global $DB;

    $context = context_course::instance($courseid);

    $roles = array();

    $records = $DB->get_recordset('role_assignments', array('contextid' => $context->id));
    foreach ($records as $record) {
        if (isset($roles[$record->userid]) === false) {
            $roles[$record->userid] = array();
        }
        $roles[$record->userid][$record->roleid] = $record;
    }
    $records->close();

    return $roles;
}

/**
 * Can user access at least one enrolled course?
 *
 * Cheat if necessary, but find out as fast as possible!
 *
 * @param int|stdClass $user null means use current user
 * @return bool
 */
function enrol_user_sees_own_courses($user = null) {
    global $USER;

    if ($user === null) {
        $user = $USER;
    }
    $userid = is_object($user) ? $user->id : $user;

    // Guest account does not have any courses
    if (isguestuser($userid) or empty($userid)) {
        return false;
    }

    // Let's cheat here if this is the current user,
    // if user accessed any course recently, then most probably
    // we do not need to query the database at all.
    if ($USER->id == $userid) {
        if (!empty($USER->enrol['enrolled'])) {
            foreach ($USER->enrol['enrolled'] as $until) {
                if ($until > time()) {
                    return true;
                }
            }
        }
    }

    // Now the slow way.
    $courses = enrol_get_all_users_courses($userid, true);
    foreach($courses as $course) {
        if ($course->visible) {
            return true;
        }
        context_helper::preload_from_record($course);
        $context = context_course::instance($course->id);
        if (has_capability('moodle/course:viewhiddencourses', $context, $user)) {
            return true;
        }
    }

    return false;
}

/**
 * Returns list of courses user is enrolled into without performing any capability checks.
 *
 * The $fields param is a list of field names to ADD so name just the fields you really need,
 * which will be added and uniq'd.
 *
 * @param int $userid User whose courses are returned, defaults to the current user.
 * @param bool $onlyactive Return only active enrolments in courses user may see.
 * @param string|array $fields Extra fields to be returned (array or comma-separated list).
 * @param string|null $sort Comma separated list of fields to sort by, defaults to respecting navsortmycoursessort.
 * @return array
 */
function enrol_get_all_users_courses($userid, $onlyactive = false, $fields = null, $sort = null) {
    global $DB;

    // Re-Arrange the course sorting according to the admin settings.
    $sort = enrol_get_courses_sortingsql($sort);

    // Guest account does not have any courses
    if (isguestuser($userid) or empty($userid)) {
        return(array());
    }

    $basefields = array('id', 'category', 'sortorder',
            'shortname', 'fullname', 'idnumber',
            'startdate', 'visible',
            'defaultgroupingid',
            'groupmode', 'groupmodeforce');

    if (empty($fields)) {
        $fields = $basefields;
    } else if (is_string($fields)) {
        // turn the fields from a string to an array
        $fields = explode(',', $fields);
        $fields = array_map('trim', $fields);
        $fields = array_unique(array_merge($basefields, $fields));
    } else if (is_array($fields)) {
        $fields = array_unique(array_merge($basefields, $fields));
    } else {
        throw new coding_exception('Invalid $fields parameter in enrol_get_all_users_courses()');
    }
    if (in_array('*', $fields)) {
        $fields = array('*');
    }

    $orderby = "";
    $sort    = trim($sort);
    if (!empty($sort)) {
        $rawsorts = explode(',', $sort);
        $sorts = array();
        foreach ($rawsorts as $rawsort) {
            $rawsort = trim($rawsort);
            if (strpos($rawsort, 'c.') === 0) {
                $rawsort = substr($rawsort, 2);
            }
            $sorts[] = trim($rawsort);
        }
        $sort = 'c.'.implode(',c.', $sorts);
        $orderby = "ORDER BY $sort";
    }

    $params = array('siteid'=>SITEID);

    if ($onlyactive) {
        $subwhere = "WHERE ue.status = :active AND e.status = :enabled AND ue.timestart < :now1 AND (ue.timeend = 0 OR ue.timeend > :now2)";
        $params['now1']    = round(time(), -2); // improves db caching
        $params['now2']    = $params['now1'];
        $params['active']  = ENROL_USER_ACTIVE;
        $params['enabled'] = ENROL_INSTANCE_ENABLED;
    } else {
        $subwhere = "";
    }

    $coursefields = 'c.' .join(',c.', $fields);
    $ccselect = ', ' . context_helper::get_preload_record_columns_sql('ctx');
    $ccjoin = "LEFT JOIN {context} ctx ON (ctx.instanceid = c.id AND ctx.contextlevel = :contextlevel)";
    $params['contextlevel'] = CONTEXT_COURSE;

    //note: we can not use DISTINCT + text fields due to Oracle and MS limitations, that is why we have the subselect there
    $sql = "SELECT $coursefields $ccselect
              FROM {course} c
              JOIN (SELECT DISTINCT e.courseid
                      FROM {enrol} e
                      JOIN {user_enrolments} ue ON (ue.enrolid = e.id AND ue.userid = :userid)
                 $subwhere
                   ) en ON (en.courseid = c.id)
           $ccjoin
             WHERE c.id <> :siteid
          $orderby";
    $params['userid']  = $userid;

    $courses = $DB->get_records_sql($sql, $params);

    return $courses;
}



/**
 * Called when user is about to be deleted.
 * @param object $user
 * @return void
 */
function enrol_user_delete($user) {
    global $DB;

    $plugins = enrol_get_plugins(true);
    foreach ($plugins as $plugin) {
        $plugin->user_delete($user);
    }

    // force cleanup of all broken enrolments
    $DB->delete_records('user_enrolments', array('userid'=>$user->id));
}

/**
 * Called when course is about to be deleted.
 * @param stdClass $course
 * @return void
 */
function enrol_course_delete($course) {
    global $DB;

    $instances = enrol_get_instances($course->id, false);
    $plugins = enrol_get_plugins(true);
    foreach ($instances as $instance) {
        if (isset($plugins[$instance->enrol])) {
            $plugins[$instance->enrol]->delete_instance($instance);
        }
        // low level delete in case plugin did not do it
        $DB->delete_records('user_enrolments', array('enrolid'=>$instance->id));
        $DB->delete_records('role_assignments', array('itemid'=>$instance->id, 'component'=>'enrol_'.$instance->enrol));
        $DB->delete_records('user_enrolments', array('enrolid'=>$instance->id));
        $DB->delete_records('enrol', array('id'=>$instance->id));
    }
}

/**
 * Try to enrol user via default internal auth plugin.
 *
 * For now this is always using the manual enrol plugin...
 *
 * @param $courseid
 * @param $userid
 * @param $roleid
 * @param $timestart
 * @param $timeend
 * @return bool success
 */
function enrol_try_internal_enrol($courseid, $userid, $roleid = null, $timestart = 0, $timeend = 0) {
    global $DB;

    //note: this is hardcoded to manual plugin for now

    if (!enrol_is_enabled('manual')) {
        return false;
    }

    if (!$enrol = enrol_get_plugin('manual')) {
        return false;
    }
    if (!$instances = $DB->get_records('enrol', array('enrol'=>'manual', 'courseid'=>$courseid, 'status'=>ENROL_INSTANCE_ENABLED), 'sortorder,id ASC')) {
        return false;
    }
    $instance = reset($instances);

    $enrol->enrol_user($instance, $userid, $roleid, $timestart, $timeend);

    return true;
}

/**
 * Is there a chance users might self enrol
 * @param int $courseid
 * @return bool
 */
function enrol_selfenrol_available($courseid) {
    $result = false;

    $plugins = enrol_get_plugins(true);
    $enrolinstances = enrol_get_instances($courseid, true);
    foreach($enrolinstances as $instance) {
        if (!isset($plugins[$instance->enrol])) {
            continue;
        }
        if ($instance->enrol === 'guest') {
            // blacklist known temporary guest plugins
            continue;
        }
        if ($plugins[$instance->enrol]->show_enrolme_link($instance)) {
            $result = true;
            break;
        }
    }

    return $result;
}

/**
 * This function returns the end of current active user enrolment.
 *
 * It deals correctly with multiple overlapping user enrolments.
 *
 * @param int $courseid
 * @param int $userid
 * @return int|bool timestamp when active enrolment ends, false means no active enrolment now, 0 means never
 */
function enrol_get_enrolment_end($courseid, $userid) {
    global $DB;

    $sql = "SELECT ue.*
              FROM {user_enrolments} ue
              JOIN {enrol} e ON (e.id = ue.enrolid AND e.courseid = :courseid)
              JOIN {user} u ON u.id = ue.userid
             WHERE ue.userid = :userid AND ue.status = :active AND e.status = :enabled AND u.deleted = 0";
    $params = array('enabled'=>ENROL_INSTANCE_ENABLED, 'active'=>ENROL_USER_ACTIVE, 'userid'=>$userid, 'courseid'=>$courseid);

    if (!$enrolments = $DB->get_records_sql($sql, $params)) {
        return false;
    }

    $changes = array();

    foreach ($enrolments as $ue) {
        $start = (int)$ue->timestart;
        $end = (int)$ue->timeend;
        if ($end != 0 and $end < $start) {
            debugging('Invalid enrolment start or end in user_enrolment id:'.$ue->id);
            continue;
        }
        if (isset($changes[$start])) {
            $changes[$start] = $changes[$start] + 1;
        } else {
            $changes[$start] = 1;
        }
        if ($end === 0) {
            // no end
        } else if (isset($changes[$end])) {
            $changes[$end] = $changes[$end] - 1;
        } else {
            $changes[$end] = -1;
        }
    }

    // let's sort then enrolment starts&ends and go through them chronologically,
    // looking for current status and the next future end of enrolment
    ksort($changes);

    $now = time();
    $current = 0;
    $present = null;

    foreach ($changes as $time => $change) {
        if ($time > $now) {
            if ($present === null) {
                // we have just went past current time
                $present = $current;
                if ($present < 1) {
                    // no enrolment active
                    return false;
                }
            }
            if ($present !== null) {
                // we are already in the future - look for possible end
                if ($current + $change < 1) {
                    return $time;
                }
            }
        }
        $current += $change;
    }

    if ($current > 0) {
        return 0;
    } else {
        return false;
    }
}

/**
 * Is current user accessing course via this enrolment method?
 *
 * This is intended for operations that are going to affect enrol instances.
 *
 * @param stdClass $instance enrol instance
 * @return bool
 */
function enrol_accessing_via_instance(stdClass $instance) {
    global $DB, $USER;

    if (empty($instance->id)) {
        return false;
    }

    if (is_siteadmin()) {
        // Admins may go anywhere.
        return false;
    }

    return $DB->record_exists('user_enrolments', array('userid'=>$USER->id, 'enrolid'=>$instance->id));
}

/**
 * Returns true if user is enrolled (is participating) in course
 * this is intended for students and teachers.
 *
 * Since 2.2 the result for active enrolments and current user are cached.
 *
 * @param context $context
 * @param int|stdClass $user if null $USER is used, otherwise user object or id expected
 * @param string $withcapability extra capability name
 * @param bool $onlyactive consider only active enrolments in enabled plugins and time restrictions
 * @return bool
 */
function is_enrolled(context $context, $user = null, $withcapability = '', $onlyactive = false) {
    global $USER, $DB;

    // First find the course context.
    $coursecontext = $context->get_course_context();

    // Make sure there is a real user specified.
    if ($user === null) {
        $userid = isset($USER->id) ? $USER->id : 0;
    } else {
        $userid = is_object($user) ? $user->id : $user;
    }

    if (empty($userid)) {
        // Not-logged-in!
        return false;
    } else if (isguestuser($userid)) {
        // Guest account can not be enrolled anywhere.
        return false;
    }

    // Note everybody participates on frontpage, so for other contexts...
    if ($coursecontext->instanceid != SITEID) {
        // Try cached info first - the enrolled flag is set only when active enrolment present.
        if ($USER->id == $userid) {
            $coursecontext->reload_if_dirty();
            if (isset($USER->enrol['enrolled'][$coursecontext->instanceid])) {
                if ($USER->enrol['enrolled'][$coursecontext->instanceid] > time()) {
                    if ($withcapability and !has_capability($withcapability, $context, $userid)) {
                        return false;
                    }
                    return true;
                }
            }
        }

        if ($onlyactive) {
            // Look for active enrolments only.
            $until = enrol_get_enrolment_end($coursecontext->instanceid, $userid);

            if ($until === false) {
                return false;
            }

            if ($USER->id == $userid) {
                if ($until == 0) {
                    $until = ENROL_MAX_TIMESTAMP;
                }
                $USER->enrol['enrolled'][$coursecontext->instanceid] = $until;
                if (isset($USER->enrol['tempguest'][$coursecontext->instanceid])) {
                    unset($USER->enrol['tempguest'][$coursecontext->instanceid]);
                    remove_temp_course_roles($coursecontext);
                }
            }

        } else {
            // Any enrolment is good for us here, even outdated, disabled or inactive.
            $sql = "SELECT 'x'
                      FROM {user_enrolments} ue
                      JOIN {enrol} e ON (e.id = ue.enrolid AND e.courseid = :courseid)
                      JOIN {user} u ON u.id = ue.userid
                     WHERE ue.userid = :userid AND u.deleted = 0";
            $params = array('userid' => $userid, 'courseid' => $coursecontext->instanceid);
            if (!$DB->record_exists_sql($sql, $params)) {
                return false;
            }
        }
    }

    if ($withcapability and !has_capability($withcapability, $context, $userid)) {
        return false;
    }

    return true;
}

/**
 * Returns an array of joins, wheres and params that will limit the group of
 * users to only those enrolled and with given capability (if specified).
 *
 * Note this join will return duplicate rows for users who have been enrolled
 * several times (e.g. as manual enrolment, and as self enrolment). You may
 * need to use a SELECT DISTINCT in your query (see get_enrolled_sql for example).
 *
 * @param context $context
 * @param string $prefix optional, a prefix to the user id column
 * @param string|array $capability optional, may include a capability name, or array of names.
 *      If an array is provided then this is the equivalent of a logical 'OR',
 *      i.e. the user needs to have one of these capabilities.
 * @param int $group optional, 0 indicates no current group and USERSWITHOUTGROUP users without any group; otherwise the group id
 * @param bool $onlyactive consider only active enrolments in enabled plugins and time restrictions
 * @param bool $onlysuspended inverse of onlyactive, consider only suspended enrolments
 * @param int $enrolid The enrolment ID. If not 0, only users enrolled using this enrolment method will be returned.
 * @return \core\dml\sql_join Contains joins, wheres, params
 */
function get_enrolled_with_capabilities_join(context $context, $prefix = '', $capability = '', $group = 0,
        $onlyactive = false, $onlysuspended = false, $enrolid = 0) {
    $uid = $prefix . 'u.id';
    $joins = array();
    $wheres = array();

    $enrolledjoin = get_enrolled_join($context, $uid, $onlyactive, $onlysuspended, $enrolid);
    $joins[] = $enrolledjoin->joins;
    $wheres[] = $enrolledjoin->wheres;
    $params = $enrolledjoin->params;

    if (!empty($capability)) {
        $capjoin = get_with_capability_join($context, $capability, $uid);
        $joins[] = $capjoin->joins;
        $wheres[] = $capjoin->wheres;
        $params = array_merge($params, $capjoin->params);
    }
…